Blocking layer cell



Aug. 31, 1943.

L. A. L. ESSELING ET AL BLOCKING LAYER CELL Filed July 2, 1941 Patented Aug. 31, 1943 UNITED STATES PATENT CFFICE BLO CKING LAYER CELL Application July 2, 1941, Serial No. 400,852 In the Netherlands July 3, 1940 (Cl. F75- 366) 4 Claims.

The invention relates to a blocking-layer cell comprising a non-genetic blocking layer in which one or more grids are embedded.

For influencing the electron current in a blocking-layer cell it is known to embed one or more grids in a blocking layer which has a non-genetic character with respect to the two main electrodes. By a non-genetic layer is meant a layer of electrically insulating material having such a thickness value that electrons can permeate therethrough substantially unimpeded. to obtain an electric field of sufficient strength between the two main electrodes, it is necessary that the relative spacing between them should be very small, of the order of a few microns. The grid or grids and the blocking layer consisting of a plurality of films must each have therefore a very slight thickness. This requirement makes it difficult to apply to one of the electrodes the various insulating films constituting the blocking layer.

It has therefore previously been proposed to dissolve the blocking-layer material in some substance or other and then to spread or to spray the dissolved material on the electrode to be coated, whereupon the solvent is expelled and a very thin film of the blocking-layer material remains behind.

This entails the following drawback. When in the above-mentioned manner the first layer has been produced and a grid has been provided thereon, the application of a second layer to the grid in the same manner causes -the material of the first layer to dissolve again, at least partly. The thickness of the layer, which previously had exactly been fixed and obtained, is liable to vary in an uncontrollable manner so that the properties of such a cell cannot be calculated beforehand. I

According to' the invention, in order to obviate this drawback, it is proposed to constitute the various films which jointly form the blocking layer, by different materials. The application of this rule affords a'greater liberty in the choice of the methods of applying the various films. example, firstly a film of polystyrene may be provided from a solution, whereupon a following lm of alumina is applied from a suspension. In the application of the second film the film formed is not influenced by these different methods.

If it is desired to utilize for the application of the blocking layer the dissolving method as described above, use may advantageously also be made of the rule given according to the invention by selecting for the successive lms materials For In order which are soluble in solvents which are not common to the different materials.

The first iilm, which consists of a determined insulating material such as' polystyrene, shellac, Canada balsam or chlorinated rubber lacquer, may be applied from a solution in a determined medium, whereupon for the application of the following insulating film use is made of another insulating material which is soluble in another medium.

In the following mode of realisation, given by Way of example, a blocking-layer cell according to the invention is described wherein also the method of its manufacture is indicated, the whole of it being illustrated by a drawing.

In the production of a blocking layer cell the starting point is formed by a supporting plate I of aluminium on which an anode 2 consisting of selenium is provided. For the production of a lm 3 which, jointly with a film 4, forms the blocking layer in which a grid 5 is embedded, polystyrene dissolved in benzene is spread out or sprayed on the electrode 2. By dosing the solution and starting from a determined concentration a pre-determined thickness of the layer 3 may be obtained. This thickness ranges in general from 1 to 5 microns.

The grid 5 is provided on the film 3 by applying thereon by vaporisation a thin layer of copper having a thickness of about 0.1 micron, which layer is exposed to the action of iodine vapour so that a conducting layer of cuprous iodide of rather bad electro-n-emissivity is produced. Owing to its slight thickness this layer is so porous that electrons can readily pass through it.

In contact with the grid is placed a strip G of copper of a thickness of about 1 micron, which serves to connect the grid to an external circuit.

To the grid is applied the second film of insulating material, use being made of a material which is soluble in a liquid in which the material of the layer 3 does not dissolve. A suitable material is, for example, shellac which dissolves in alcohol and ketones. Other materials suitable for producing films are the following: Canada balsam, which is soluble in turpentine, or chlorinated rubber lacquer which is soluble in xylene, acetone and toluene, phenol-formaldehyde condensation products which dissolve in alcohol, or again a plasticized phenol resin soluble in benzene hydro-carbides. This resin may be obtained by condensation of a phenol alcohol with a mono-alcohol and is heated for some time, for example with wood oil, said resin being dissolved I therefoe im 'Ehe above-mentioned pumas@ e '131e sf Biloxi lem he eheve-mentiomed me,-

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